The Core will provide scientific and administrative leadership for the program as a whole. It will coordinate the research and seminar activities, and maintain a communication network among the projects, projects and core, and projects an the scientific coordinator. The Core provide essential service function. Specifically; Specific Aims 1. To provide administrative and scientific leadership to the program including coordination of activities among the 3 projects. 2. To generate and provide regular supply of viable, clean, purified and concentrated Cryptosporidium parvum oocysts required for the program. 3. Perform all the in vivo and some of the n vitro studies required for the program. The above services are essential for the performance of all 3 projects and the Core.